The cellular, biological and immunological factors in peripheral nerve regeneration are being studied in a rat vein-graft model. The vein graft serves as a chamber into which various biologic agents such as collagen or "trophic" factor such as nerve growth factor as well as specific cell types grown in tissue culture can be added to study their effects on axonal regeneration. Quantitative light and electron microscopic measures are being utilized to analyze the effects. To date, human tumor cells in the vein-graft have enhanced regeneration wheras microcrystalline collagen has inhibited the process. The influence of fetal dorsal root ganglion cells, cerebellar cell, cortical cells, and fibroblasts are currently under study.